Preparing your spreadsheet for import
Kanon Maps only reads one column of your spreadsheet: the postcodes. Everything else stays on your computer. Here's how to prepare a file that imports smoothly — and why trimming it first is good privacy practice.
What the import needs
- A CSV or Excel (.xlsx) file, up to 5MB.
- A header row — the first row should name each column.
- One column containing UK postcodes. It doesn't matter what it's called or where it sits; you'll pick it during the import.
Blank postcode cells are skipped, and anything that isn't a valid UK postcode is listed back to you after the import so you can fix it and re-upload just those rows.
If your Excel file is over the limit
Postcodes themselves take almost no space — a plain list of thousands of them is a tiny file. When an Excel file is too big to upload, the size is nearly always coming from everything around the postcodes:
- Extra columns — names, addresses, notes and other member details the import never uses.
- Formatting — cell colours, borders and conditional formatting across large ranges.
- Images and charts — logos or embedded graphics anywhere in the workbook.
- Phantom rows and columns — Excel remembering thousands of empty cells that were once touched, long after they were cleared.
- Extra worksheets — other tabs in the same workbook, even ones you'd forgotten were there.
The fix: copy the postcodes into a fresh file
Rather than hunting down each culprit, start clean — it takes under a minute:
- Open a new, blank workbook.
- In your original file, select the postcode column (click its column letter) and copy it.
- Paste it into the new workbook using Paste Values, so no formatting comes along.
- Check the first cell is a header (for example, “Postcode”) and save.
Saving the new file as CSV instead of .xlsx works just as well and produces the smallest possible file — a CSV of postcodes essentially can't reach the upload limit.
Less to upload, less to trust us with
Kanon Maps never stores postcodes — each one becomes an approximate point and is discarded — and the import ignores every column except the one you pick. But the best data protection is data that never leaves your computer at all. Trimming your spreadsheet to just the postcode column means names, addresses and notes are never uploaded in the first place.